The present invention relates generally to the field of disc drive data storage devices, and more particularly but not by way of limitation, to a compressive limit stop for limiting the movement of an actuator while dissipating energy following contact of the actuator with the compressive limit stop in a data storage device.
Disc drives are data storage devices that enable users to rapidly store and retrieve data. Typically, a head/disc assembly (HDA), which houses requisite mechanical portions of the drive and a printed wiring assembly (PWA), which supports requisite electronic portions of the drive comprise a disc drive.
The HDA includes a base deck to which various components are mounted and a top cover cooperating with the base deck to form a sealed housing to reduce particulate contamination. Within the housing, a disc stack is typically formed from a recording disc axially aligned about a spindle motor that rotates the recording disc at a constant, high speed, such as 10,000 revolutions per minute during normal disc drive operation.
A rotary actuator assembly is mounted adjacent the disc stack and includes a ridged arm supporting a flexible suspension assembly, which in turn supports a read/write head communicating with a recording surface of the disc.
The read/write head is typically position-controlled over a pre-selected data track of the recording surface through the interaction of the actuator assembly and a voice coil motor. For data storage devices utilizing magnetoresistive head technology, the read/write head typically includes a thin-film inductive write element to write data to the recording surface and a magneto-resistive (MR) read element to read previously written data from the recording surface.
When the disc drive is not in use, the read/write head is typically landed and brought to rest in a parking zone, which is generally located near the inner diameter of the recording surface. In landing the read/write head, the read/write head is flown over the parking zone and the rotation of the spindle motor is stopped.
Once the heads are positioned in the parking zone, it is typically advantageous to secure the actuator assembly by a latching arrangement to prevent the read/write head from subsequently moving out onto the data storage zone of the disc while the disc drive is non-operational. Latching arrangements are generally practiced in the art and have included various configurations of springs, solenoids and magnets to secure and release the actuator assembly. For example, see U.S. Pat. No. 5,187,627 issued Feb. 16, 1993, to Hickox et al; U.S. Pat. No. 5,224,000 issued Jun. 29, 1993, to Casey et al; and U.S. Pat. No. 5,231,556 issued Jul. 27, 1993, to Blanks.
While operable, such prior art latching systems suffer from several limitations. Mechanical latches typically are complex while electromechanical latches require substantial electrical power to operate. Many magnetic latches with open magnetic circuits exert considerable force when the actuator is near the magnetic latch, while the read/write head remains over the data region, thus resulting in increased power consumption. Moreover, such force can limit the maximum holding force generated by the latch.
Still other prior art latches such as inertial latching mechanisms can be ineffective upon application of a mechanical shock to the system. In particular, the contact surfaces of the latch mechanism and the moving portion of the actuator assembly are encouraged in opposing directions in response to applied mechanical shocks. Therefore, the accelerations imparted to the latching mechanism and to the moving portion of the actuator assembly can cause the contact surfaces to meet with a greater degree of force, resulting in xe2x80x9cbouncexe2x80x9d at the contact surface, which tends to overcome the latching mechanism and thereby disengage the latching mechanism.
In conjunction with providing effective latching of the actuator assembly as the disc drive comes into the non-operational mode, it is often advantageous to limit the actuator assembly movement to prevent inadvertent actuator assembly arm/gimbal assembly and disc contact. It is generally important to control the extent of actuator assembly travel relative to the non-data zones; otherwise, an actuator assembly that travels beyond the desired extent of radial travel likely results in damage to the read/write head. The inner extent of radial travel allows the read/write head to travel inwardly past the inner most data track to the landing zone where the read/write head can be parked on the disc surface when the disc drive is inoperable. Inward travel beyond this inner extent of travel can result in damaging contact of the read/write head with a hub of the spindle motor. The outer extent of radial travel allows the read/write head to access the outer most data track of the recording surface. Outward travel beyond this outer extent of travel can result in the read/write head moving beyond the outer edge of the data disc, which can damage and disable the read/write head.
As requirements for faster data processing demand ever increasing actuator assembly speed and associated deceleration rates during seek cycles, the likelihood of overshooting the target track increases. Such an overshoot near the extents of travel can result in damage to the read/write head. Also, control circuit errors are known to create xe2x80x9crunawayxe2x80x9d conditions of the actuator assembly wherein the actuator assembly fails to decelerate at the appointed time. To protect the read/write head from catastrophic failure, it is well known and practiced in the art to employ positive stops which limit the actuator assembly travel to locations only between the desired extents of travel.
In providing such a positive stop, or limit stop, it is necessary that the limit stop decelerate the actuator assembly quickly and in a short distance, but without damaging the actuator assembly. Applying a general dampened braking impulse is known in the art, such as by the use of an air cylinder type dampener as taught by U.S. Pat. No. 4,937,692 issued to Okutsu. In this approach fluid is displaced by a piston that is responsive to a stop member that obstructs the movement of the actuator assembly beyond the desired extent of travel. The dampened braking impulse provides a resistive force for decelerating the actuator assembly, but without the typical sudden deceleration of a rigid stop member, such as a rigid stop pin.
Manufacturability and cost constraints have urged the art toward more simple mechanisms. The use of a resilient pad is widely known, such as that of the teaching of U.S. Pat. No. 4,890,176 issued to Casey et al. and assigned to the assignee of the present invention. Spring members, too, are widely used in the art, such as that according to the teaching of U.S. Pat. No. 4,635,151 issued to Hazebrouck. The primary objection to resilient pads and springs, however, is the relatively long stopping distances necessary to compress the responsive member sufficiently so as to develop an effective braking force.
One attempted solution is to provide a preload force to the resilient member, such as is taught by U.S. Pat. No. 4,949,206 issued to Phillips et al. Another approach is to provide cantilever members that elastically deflect in response to the impact force of the actuator assembly, such as is taught by U.S. Pat. No. 5,134,608 issued to Strickler and U.S. Pat. No. 5,600,516 issued to Phillips et al. and assigned to the assignee of the present invention. Where the resilient member provides a superior initial impact response in not significantly increasing the peak deceleration rate, the relatively large amount of disc space necessarily reserved for stopping distance runs counter to the efforts in maximizing disc space utilization.
Consequently, there has not been available a latching device nor a limit stop which will universally meet the ever increasing demands of disc latching and actuator assembly movement control in reducing the susceptibility of damage to the disc drive. It is to such ends that the present invention is directed.
As exemplified by preferred embodiments, a compressive limit stop for limiting travel of an actuator assembly of a data storage device is disclosed. The compressive limit stop separates a first pole piece from a second pole piece of the data storage device, each pole piece adjacent the actuator assembly, the compressive limit stop comprising a rigid body with a top flange adjacent the second pole piece and a bottom flange adjacent the first pole piece, an inner portion having a diameter less than the diameter of the top flange disposed between the top and bottom flanges forming a channel between the flanges and a compressive sleeve with an inner wall adjacent each flange while enclosing the channel to form a gap between the inner portion and the inner wall. The gap between the inner portion and the inner wall extends between the top flange and the bottom flange. The compressive sleeve restricts movement of the actuator assembly upon contact of the actuator assembly with the compressive sleeve by deflecting and compressing between the actuator assembly and the inner portion to decelerate movement of the actuator assembly upon contact of the actuator assembly with the compressive sleeve.
The advantages and features of the present invention will be apparent from the following description when read in conjunction with the drawings and appended claims.